Display device and display method

ABSTRACT

The invention concerns a device for displaying an image directly on the retina ( 6 ) of the eye ( 5 ). The device comprises means ( 1 ) arranged to emit laser radiation and modulating means ( 2 ) arranged in the beam path between the laser-radiation-emitting means ( 1 ) and the eye ( 5 ) so as to modulate the laser radiation. The device is characterized in that the modulating means ( 2 ) are arranged so as to modulate the phase front of the laser beam so that, when it strikes the refracting elements of the eye, it is deflected in a direction distinct from the direction obtained with unmodulated radiation. The invention also includes a method of displaying a retinal image.

TECHNICAL AREA

This invention concerns a device for producing an image directly on theretina of the eye as per the preamble to claim 1.

The invention also concerns a corresponding method for producing aretinal image.

STATE OF THE ART

When information is to be displayed, an image plane on which theinformation is projected is often used. The image plane can consist of,e.g. a TV screen, monitor or the like. However, methods also exist tobuild up an image on the retina of the eye that do not require that theimage information be supplied via an image plane.

U.S. Pat. No. 6,008,781 describes a system that projects a virtual imagedirectly onto the retina without the use of an image surface. The systemcomprises a photogenerator arranged so as to emit radiation. Thephotogenerator consists of, e.g. a laser or includes LED diodes, whichemit red, green and blue light. The system further comprises means formanipulating the emitted radiation to create video-modulated signals.The video-modulated signals can be scanned both horizontally andvertically to create a modulated light raster, which is projecteddirectly onto the eye of the user via projection optics. It is necessaryfor the projection optics to be arranged in such a way that the eyepoints directly toward the incident video-modulated signals, which meansin practice that the projection optics, in the form of, e.g. mirrors,must be positioned so that the eye is looking directly at them. Theaforedescribed system is also extremely sensitive to interference andrequires that the manipulated beam be pointed precisely at the eye, andthat the beam lobe of the radiation be narrow enough that the entirebeam can pass through the pupil of the eye to strike the retina.

DESCRIPTION OF THE INVENTION

One object of the invention is to eliminate the need for positioningequipment such as the aforedescribed projection optics centrally infront of the eye. Another object of the invention is to solve theproblem of sensitivity to interference.

According to one embodiment, this is achieved by means of a devicecomprising means arranged to emit laser radiation, plus modulating meansarranged to modulate the laser beam that are arranged in the beam pathbetween the laser-radiation-emitting means and the eye. The device ischaracterized in that the modulating means are arranged so as tomodulate the phase front of the laser beam in such a way that, uponstriking the refracting elements of the eye, the beam is deflected in adirection that is distinct from a direction obtained with unmodulatedradiation.

Using this device, a retinal image can be created in at least twodifferent ways. According to the first such way, the modulating means ofthe device are arranged so as to modulate the phase front of the laserbeam in such a way that, upon deflection, the beam is focused on adefined point on the retina of the eye, while the modulating means arefurther arranged so as to continuously remodulate the laser beam so asto move this point in order to build up the retinal image.

According to the second such way, the modulating means of the device arearranged so as to modulate the phase front so that the beam contains, ateach moment in time, information for producing the entire retinal image.

To eliminate the necessity of positioning the equipment centrally infront of the eye, the modulating means are arranged relative to the eyein one advantageous embodiment in such a way that the modulated laserbeam strikes the eye at an angle distinct from the optical axis of theeye, while the modulated means are arranged so as to modulate thewavefront so that it is deflected in such a way that the beam isprojected onto the retina centrally around the optical axis.

To render the device less sensitive to the positioning of the eyerelative to the incident laser beam, the beam lobe has, at the eye, across-section that is larger than 3 cm², e.g. 5 cm².

In a preferred embodiment, the modulating means comprise a so-called SLM(spatial light modulator) and controlling means arranged to control theadjustment of the spatial light modulator. To summarize briefly, thespatial light modulator can display patterns that consist of quantizedphase patterns (pixelated) and function as a phase/amplitude converterfor laser radiation. A spatial light modulator is thus a phase/amplitudemodulator, wherein the intensity and phase of the incident laserradiation can be controlled for each pixel of the light modulator. Byusing the spatial light modulator for combined phase and possibleamplitude modulation of the cross-section of the incident laser beam,the laser beam is made capable of refraction into an image of an objector to a given point upon passing through one or a plurality ofrefracting elements.

The invention also includes a method according to claim 9.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 shows an example of an image-display system according to theinvention,

FIG. 2 a shows unmodulated laser radiation that is striking the retinaof the eye,

FIG. 2 b shows modulated laser radiation that is striking a point on theretina of the eye,

FIG. 2 c shows modulated laser radiation that is striking a surface onthe retina of an eye,

FIGS. 3 a, b and c show an example of control of the modulated beam inFIG. 2 b in the eye,

FIG. 4 shows an exemplary use of modulated radiation to create a virtualdisplay in a mobile telephone application,

FIG. 5 shows an exemplary installation of the image-display system ineyeglass frames,

FIG. 6 shows an exemplary use of the image-display system in a displayscreen application,

FIG. 7 shows an example of the image-display system in a wide-angleapplication.

EMBODIMENTS

Reference number 1 in FIG. 1 designates a laser that is emitting a laserbeam 4 at a spatial light modulator 2 (SLM) at a fixed angle. In theexample shown, the light modulator is of the reflecting type, but itcould also conceivably consist of a light modulator of the transmittingtype, in which case the laser 1 would be disposed behind the lightmodulator. There is connected to the light modulator 2 a calculatingunit 3 in the form of, e.g. a personal computer, which is arranged so asto affect the adjustment of the phase pattern of the light modulator 2.The laser 1 and the light modulator 2 are positioned relative to oneanother in such a way that the radiation modulated by the lightmodulator 2 strikes an approximate position where an eye 5 is expectedto be present. The incident beam is refracted by the refracting elements8 of the eye so as to be focused on the retina of the eye. Therefracting elements of the eye essentially consist of the cornea andlens of the eye, but they also include the intraocular fluid and thevitreous body.

In FIG. 2 a, unmodulated radiation as per the state of the art strikesthe refracting elements 8 of the eye so as to be focused at a point onthe retina of the eye as determined by the geometry of said refractingelements. The intensity pattern of the unmodulated beam exhibits aGaussian distribution at said point.

In FIG. 2 b, modulated radiation strikes the refracting elements 8 ofthe eye and is refracted in a direction determined by the phase front ofthe laser beam toward a point on the retina of the eye determined bysaid direction. In this embodiment, the intensity pattern of themodulated beam exhibits a Gaussian distribution at said point.

In FIG. 2 c the modulated beam strikes the refracting elements 8 so as,in similarity with the embodiment described in connection with FIG. 2 b,to be refracted to a position determined via the phase modulation.Furthermore, the refracting elements reform the laser beam so that itassumes an intensity pattern that is also determined by the phasemodulation. It should be noted that, when the beam is phase-modulated, aphase hologram is produced in the cross-section of the beam. As aresult, the laser beam need not be centered on the eye to produce animage on the retina. It suffices for the eye to be somewhere in thelaser lobe for the image to be produced on the retina. How great aportion of the laser lobe must pass through the pupil of the eye dependson the resolution quality that can be obtained from the light modulator.Low resolution in the phase hologram demands that a greater portion ofthe energy of the laser beam strike the retina, whereupon a largerportion of the phase information of the beam will be utilized.Conversely, a smaller portion of the phase information is used inconnection with a high-resolution hologram, i.e. an acceptable image canbe produced on the retina using a smaller portion of the laser lobe.

In the embodiment shown in FIG. 1, the laser beam is modulated in such away that it is refracted by the refracting elements so that the beam isfocused on the retina 6 of the eye along an axis that is coincident withthe optical axis 7 of the eye. Thus, neither the light modulator nor theprojection optics that control the modulated laser beam from the lightmodulator needs to be arranged along the optical axis of the eye.

In FIG. 3 a the laser beam 4 strikes the eye at an angle α relative tothe optical axis of the eye. The calculating unit 3 is arranged tofurnish data for adjusting the light modulator 2 so that the laser beamrefracts, by means of the refracting elements 8 of the eye, themodulated laser beam so as to focus it on a defined point on the retinaof the eye, and so that the laser beam is continuously remodulated tomove this point in order to build up the retinal image. FIG. 3 b showshow an angle β between the incident beam and the refracted beam variesover time in the x-direction, while the angle of incidence α remainsessentially constant over time. FIG. 3 c shows how the angle β variesover time in the y-direction. As noted above, it is not critical for theeye to be placed exactly along the line of symmetry of the modulatedlaser beam; the eye needs only to be positioned somewhere within thelaser lobe in order to be able to focus an accurate image on the retina.For example, the width of the beam lobe is greater than 3 cm, andgreater than 5 cm in an alternative embodiment in which the eye is notexpected to remain entirely motionless relative to the incident laserbeam. To achieve a desired beam lob, the modulator can modulate the beamso that it has the desired width at the eye or, alternatively, a lens(not shown) that disperses the beam in the desired way can be arrangedin the beam path after the modulator 2.

The adjustment of the light modulator 2 can alternatively be such thatthe deflected beam forms the entire retinal image at each moment intime. As noted above, it is not decisive for the entire laser beam topass through the pupil of the eye in this embodiment either.

The production of hardware and/or software for the calculating unit 3used to calculate the surface pattern of the light modulator to producea desired modulation of the laser beam is not within the scope of thisinvention. The creation of software/hardware to calculate the phasepattern of the light modulator needed to achieve a desired modulation ofthe laser beam will be a routine procedure to one skilled in the art.The design of the functions and algorithms in the software/hardware isdetermined by a number of parameters, such as the material used for thephase pattern in the light modulator, the type of laser, the laserwavelength used, etc.

In FIG. 4 the laser source 1 and the light modulator 2 are built into amobile telephone 10, whereupon modulated laser radiation is emitted fromthe mobile telephone 10 via an opening 9, which is square in the figureand characteristically has a cross-section of 1.5×1.5 cm. The modulatedlaser beam will then draw an image at full computer display resolutionon the retina 6 of the eye 5 when the mobile telephone is held at agiven distance in front of the eye.

In FIG. 5 a the laser 1 and the spatial light modulator 2 are secured inthe earpiece 13 of eyeglass frames 12. The modulated laser beam isreflected toward the eye by a mirror 11 arranged on the eyeglass frames12 roughly in front of the eye. FIG. 5 b shows a biocular design inwhich each earpiece 13 contains a laser 1 and a light modulator 2, andwherein a mirror 11 is arranged in front of each eye to reflect towardits associated eye.

In FIG. 6 the laser 1 and light modulator 2 are used to create a virtualdisplay screen. A preferably dark plate 14 is, in the example shown,placed in front of the user to increase the image contrast. In thisembodiment, an eyetracker (not shown) can be connected to thecalculating unit. The calculating unit will then be arranged so as tocalculate the modulation angle from the light modulator based on theposition of the eye in order to position the image on the plate at eyeheight. Conceivable applications include PC screens and displays builtinto aircraft pilot seats. A three-dimensional display is achieved if alaser with its associated light modulator is provided for each eye.

In FIG. 7, six lasers with their associated light modulators arearranged in a semicircle around the head of an person. Two eyetrackers15 are also arranged in front of the user. These eyetrackers 15 andlasers with their light modulators are used to create a wide-angleimage, wherein the image is also seen in the peripheral vision. Thelasers, light modulators and eyetrackers are fixedly mounted in, e.g. anaircraft cockpit.

1. A device for displaying an image directly on the retina of the eyeand comprising: means arranged so as to emit laser radiation; andmodulating means arranged to receive a laser beam from thelaser-radiation-emitting means and transmit a modulated laser beamdirectly to the eye by modulating the laser radiation, wherein in thatthe modulating means is arranged so as to modulate the phase front ofthe laser beam in such a way that, when the modulated laser beam strikesthe refracting elements of the eye, it is deflected in a directiondistinct from the direction obtained with unmodulated radiation and whenthe modulated laser beam strikes the eye at an angle distinct from anoptical axis of the eye and is deflected by said refracting elements,the modulated laser beam is projected on a retina of the eye.
 2. Thedevice according to claim 1, wherein the modulating means are arrangedso as to modulate the phase front of the laser beam in such a way that,upon deflection, the beam is focused on a defined point on the retina ofthe eye, and in that the modulating means are arranged so as tocontinuously remodulate the laser beam in order to move said point tobuild up the retinal image.
 3. The device according to claim 1, whereinthe modulating means are arranged so as to modulate the phase front insuch a way that the beam contains, at each moment in time, informationfor producing the entire retinal image.
 4. The device according to claim1, wherein in that the modulating means are arranged relative to the eyein such a way that the modulated laser beam strikes the eye at an angledistinct from the optical axis of the eye, and in that the modulatingmeans are arranged so as to modulate the wavefront so that it isdeflected in such a way that the beam is projected onto the retinacentered around the optical axis.
 5. The device according to claim 1,wherein in that the modulating means comprise an arrangement involvingat least one spatial light modulator.
 6. The device according to claim1, wherein it has means to disperse the modulated beam lobe so that itscross-section at the eye is larger than 3 cm².
 7. The device accordingto claim 5, wherein it has means to disperse the modulated beam lobe sothat its cross-section at the eye is larger than 5 cm².
 8. The deviceaccording to claim 5, wherein the dispersing means consist of saidspatial light modulator arrangement.
 9. A method for displaying an imagedirectly on the retina of an eye, the method comprising: receiving laserradiation, modulating the laser radiation and aiming the modulated laserradiation directly at a person's eye, wherein a phase front of themodulated laser radiation is modulated so that, when it strikes therefracting elements of the eye, the modulated laser radiation isdeflected in a direction distinct from that obtained with unmodulatedradiation and where the phase front of said modulated laser radiation ismodulated so that, when the modulated laser radiation strikes the eye atan angle distinct the optical axis of the eye and is deflected by saidrefracting elements, the modulated laser radiation is projected on aretina of eye.
 10. The method according to claim 9, wherein in that thephase front is modulated in such a way that, upon deflection, the beamis focused on a defined point on the retina of the eye, and in that thephase front is continuously remodulated so that the defined point moves,thereby building up the retinal image.
 11. The method according to claim9, wherein in that the phase front is modulated in such a way that thebeam contains, at each moment in time, information for producing theentire retinal image.
 12. The method according to claim 9, wherein themodulated laser beam strikes the eye at an angle distinct from theoptical axis of the eye, and in that the phase front is modulated insuch a way that, upon deflection, the beam is projected onto the retinacentrally around the optical axis.
 13. The method according to claim 9,wherein, upon modulation, the beam lobe of the beam is dispersed so thatits cross-section at the eye is larger than 3 cm².
 14. A methodaccording to claim 13, wherein it has means to disperse the modulatedbeam lobe so that its cross-section at the eye is larger than 5 cm².